text:
how does the rudder work?
What do you know about yaw control and more precisely about the result caused by the rudder (R on picture)?
Below the right pedal of the airplane has been depressed, and the rudder creates a rotation around the yaw axis and generates an aerodynamic result (R on picture) to the left on the vertical tail. Can you develop how this result is create?

https://www.lavionnaire.fr/CelluleGouvernes.php

I modified your question to fix some grammar errors. However, I still don't understand what you're asking...

why when the rudder is shifted to the right, the plane is deviated in the same direction. what is the effect of the rudder's direction? a change in the air flow?

The irony is not lost in this thread. But seriously, what is the question? If you press the right rudder pedal, the rudder will deflect to the right (starboard) side of the plane. The tail will yaw (clockwise) around to the left (port) side of the Center of Gravity. The nose will subsequently yaw (clockwise) around to the right side of the CoG. If you press the left rudder pedal, the plane will yaw counter-clockwise. The degree of yaw will be related to the force of the relative wind, the amount of rudder deflection, and the length of the moment arm of the rudder from the CoG.

Are you sure that when you depressed the right pedal the aircraft turn to the opposite direction?

Yes, if you press the right rudder pedal, the airplane will yaw clockwise as viewed from above it. That means that the nose of the airplane will yaw towards the right. See my answer below.

You should must a precise question in the title so that it is easier to navigate through the website without opening each question and because this is a Q&A website.

"Are you sure that when you depressed the right pedal the aircraft turn to the opposite direction?"  No, he is saying the exact opposite.  Right rudder = yaw right, not left.  Look at the diagram and think about it.  It works just like the rudder of a boat.  Try it with your hand in the bathtub.

Is it better yet?

When the rudder is deflected, it creates a "lift" on the vertical tail due to additional camber. This "lift", when viewed from the airplane perspective, is a side force opposite to the direction of the rudder deflection. Since the centre of pressure of this side force is aft of the centre of gravity, it generates a net yaw moment on the airplane.

For example, a right rudder deflection generates a left side force, which generates a nose right yawing moment, pulling the aircraft nose right.

Since the side force is relatively small in the big scheme of things, the airplane motion is essentially unchanged. As soon as the airplane nose begins to yaw, the airplane begins to have finite sideslip against the incoming airflow. This sideslip generates a side force that opposes the rudder force (from an increased airflow incidence against the vertical tail), as well as a yawing moment that opposes the yaw moment from rudder (i.e. a restoring moment).

For example, a right rudder generates nose right yaw motion, which creates a sideslip that produces a nose left yaw moment.

For a finite rudder deflection, the airplane begins to accumulate sideslip, until such a point that the restoring moment balances out the rudder moment.

Ok so On an aircraft the rudder is used primarily to counter adverse yaw but not to turn the airplane. A rudder operates by redirecting the fluid past the hull or fuselage, thus imparting a turning or yawing motion to the craft.

Is it correct ? Yaw is the result of high air pressure?https://i.pinimg.com/originals/12/7c/f8/127cf8ddfeeeb95ce3b8de542f443ab6.gif

@L'aviateur I prefer to say that rudder causes a lower pressure on other side, sucking the vertical stabilizer. But for intuitive thinking, sure. Rudder has many roles other than to counter adverse yaw during coordinated turn. But yes, rudder is rarely used to initiate course change.

Thanks you for your awnser

@L'aviateur - FYI, the rudder’s primary purpose is to indeed counter adverse yaw. It will also yaw the nose of the aircraft independent of adverse yaw. Doing this will increase the airspeed of the wing on the outside of the turn created by the yawing motion and decrease the airspeed of the wing on the inside of the turn. This airspeed difference will create more lift on the outside wing than on the inside wing, banking the aircraft. This bank will turn the plane without creating adverse yaw. A great tool during slow flight or to affect minute course corrections.

@JZYL - Sorry, just saw your response to L’aviateur.

http://accrodavion.be/Accrodavions/images/stabilite%20en%20lacet.gif

@L'aviateur - to give an example of how rudder can also be used to bank without creating adverse yaw, research stall/spin recovery or more specifically, the Falling Leaf Maneuver. A great tool to have/know when you need it. Especially during slow flight when you have less aileron authority.

the newton law(3) that some think of the origin of the lift also works in this case: the flow is deviated towards the right what creates a reaction on the left (lift)

Let us continue this discussion in chat.

@L'aviateur - There is an increase of air pressure on the right side of the rudder when it is deflected to the right. This is a pushing force. There is also a decrease of air pressure due to the change in airfoil camber of the elevator and angle of attack. This decrease in air pressure is a suction (Pulling) force. This is effectively lift in the horizontal reference to the left.

The rudder, being a vertical variable camber wing, applies a left lift force when displaced right.  The left lift force yaws the plane right and also applies a force trying to slew the plane to the left.  The yaw results in the relative wind striking the side of the fuselage, creating a certain amount of lift to the right, depending on how effective an airfoil the fuselage is (some more than others).  The lifting force applied to the fuselage is added to by the offset thrust line due to the yaw, also providing a lateral force to the right.
The result is the side lift of the fuselage plus the offset thrust line is more than the left side force of the rudder, and the plane slips sideways to the right, and since it's going forward as it does so it turns, although inefficiently.

It's easier to visualize if you think of an aerobatic airplane in an airshow that flies past you flying at a 90 degree bank, or flying "knife edge".  The wings are completely unloaded and are doing nothing except acting like big fins. The offset thrust line of the high powered engine, and the lift generated by the plane's fuselage, is enough to hold up the entire weight of the plane, even though the rudder at the back is pushing "down" like an elevator on a flying wing.
Roll the Extra aerobatic airplane back to level flight and do the same thing, and you get a skid-turn to the right from the rudder pushing the tail to the left.

This good answer could be perhaps be even more improved by noting that the rudder acts at a long moment-arm from the CG and thus only a relatively small force A is needed to generate the torque that maintains the sideslip angle against whatever torques are opposing it.  B is the main thing (or only thing?) that is opposing the sideslip, and includes a contribution from the fixed vertical fin, but the overall moment-arm for B is much smaller than for A, so B must be much larger than A for the torques to balance out.

If you press the right rudder pedal, the rudder will deflect to the right (starboard) side of the plane. This action will deflect the relative wind towards the right-side of the airplane much the same as if you were to turn the entire vertical stabilizer counter-clockwise. This deflection to the right generates a force acting towards the left.
The tail will yaw (clockwise) around to the left (port) side of the Center of Gravity. The nose will subsequently yaw (clockwise) around to the right side of the CoG. This will be due to the force imparted to the rudder/vertical stabilizer assembly by the angle of attack of the relative wind.
If you press the left rudder pedal, the plane will yaw counter-clockwise.
The degree of yaw will be related to the force of the relative wind, the amount of rudder deflection, and the length of the moment arm of the rudder from the CoG. The faster the relative wind is, the more force will be imparted on the empennage. The more the rudder is deflected, the more force is imparted on the empennage. The denser the air, the more force is imparted on the empennage. The greater the distance from the center of gravity to the vertical stabilizer, the more the force imparted on the empennage will create movement through the greater torque (moment) on the aircraft around the y-axis located at the CoG.

Thanks to the awnser but why "The tail will yaw (clockwise) around to the left (port)" ?because of the strength of the flux against the rudder (at right if it's deviated to the right)?

@L'aviateur - The vertical Stabilizer is like a wing mounted in an up and down orientation. The rudder is like an aileron or flap.  If you deflect the air moving past that vertical wing to the right, it will creat force towards the left. It will also create lift towards the left. Get in a car driving at 100 kmh. Stick your hand out of the window. Turning your hand thumb-side (leading edge) up will make your hand rise. Now, stick your hand out of the sunroof.  Turning your hand thumb-side (trailing edge in this case) right will move your hand to the left.

Ok thank you for you awnser

A very simple explanation here. Turning the rudder to the right is initially very similar to turning the rear tires of a forklift to the same direction.
It will make the plane tail pull left and creates the yaw.
Of course soon the similarity ends because of the interplay of fuselage with the wind and the fact that rudder forces want to roll the plan counterclockwise around its length.
But that image should give an intuitive motivation.


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What are the major aircraft systems (LRUs) using the ARINC429 Protocol?
I want to know the different aircraft systems (LRUs) using ARINC429 protocol.
Why is it used instead of the ARINC 629 ?
How is it different from the different ARINC protocols like 629 and AFDX(664)?

Why do you need to know this?  There isn't much difference between use cases for ARINC 429, 629, and AFDX besides age of the system, so I'm not sure how to provide a meaninful answer besides what user40476 has already provided.

@srihari, I have updated my answer giving you the required list.

On modern aircraft all equipments that needs to communicate to each other in binary format may use ARINC 429 protocol. For instance all fly by wires computers on Airbus 320, 330, 340 use arinc 429 protocol.
Nowadays other protocols do exist too such as arinc 629 protocol or fiber optic protocols etc.
As a summary all aircraft systems that need to transmit and receive binary data may use 429 protocol, but other digital protocols are possible.
However a standardized LRU that doesn’t use ARINC 429 protocol is the FDR ( flight data recorder), because the data that it receives is already sequentially ordered, the label is not transmitted with the data value
On the following website starting page 43 you find all the possible equipment that may use A429
http://read.pudn.com/downloads111/ebook/462196/429P1-17_Errata1.pdf
Also in the same document starting page 13 you have the list of the parameters that may be transmitted on A429
Hope this added information is helpful

I got the answer from the above

Many LRUs have capabilities to send and receive on one or more of the protocols you have specified. Depending on the age and necessity/capabilities of the system, they might have interfaces for one or all. There are also CAN bus standards and others. Each protocol offers a similar approach to data transfer with unique capabilities for each, for example AFDX can implement redundancy and broadcast-like abilities through Virtual Links while A429, while older, is in wider use. If you could refine  you question so it is not so broad, I'm sure I could give you a more detailed answer.

I hope you understand my question. What are the aircraft systems  using the ARINC 429 Protocol

@srihari, if you require a full list of all systems, currently in use, in all aircraft...well, we would have a massive list, as most everything utilizes A429 in some manor whether it be data acquisition or data loading. I wish I could provide you with a comprehensive list but i'm more on the software side when dealing with the protocols and cannot provide a detailed list, i'm sorry. However if you do have specific functionality questions, i may be able to assist there. If you do really need the full list of LRUs implementing A429 it may be easier to compile a list of units that dont use it.

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text:
Proportionally, what is more affected by a hot and high takeoff - a electrically driven propeller or a turbofan?
My assumption would be the electrically driven propeller would be less affected compared to turbofans at high altitudes and take off as although the air would be less dense at these ambient conditions, the electric motor itself should be unaffected. In a turbofan my assumption would be that both combustion efficiency in the core and propulsion efficiency by the fan would be negatively affected.
Is this assumption correct?

Combustion efficiency would not be affected, but the maximum power would as it would only be able to burn less fuel in the less available air.

Is this assumption correct?

Generally, yes. However, specific combinations of powerplant and propeller might make that difference moot.

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text:
How is the wing area of an airplane determined?

Picture source is from here.
Here are wing areas of several airplanes. As we can see the Spitfire, B747-400, and Mirage 2000, their wing area are not rectangular. The line drawn from left side to the right side of the fuselage are not parallel to their fuselage's cross-section, or they are not perpendicular to the fuselage. The connecting line in the drawing of the Spitfire is curving (bulge) on the trailing edge side, while the B747-400 and the Mirage 2000 have pointing shape on the leading edge side. As we know that the wing area (hence also affects the aspect ratio) is very critical to an airplane to make it fly as wing area is included in the lift formula, so, what I want to ask here are:

Is that depiction correct? If it is correct, then my further question is, why does not all the airplane body (except the horizontal stabilizer) considered as wing area?
If it is not true, then how should I determine the wing area?

So far, what I found in many explanations is that the wing is the area from root to the wing tip times two, both sides calculated then times two as there area two wings, left and right. With the information in that link then all calculation will be changed: both wing area and the aspect ratio will be changed, calculation will be affected.
===============
Edit/Added:
There is a good article here explains about wing area. Based on that article, neither the first nor the second question is true as there is no solid method about how to calculate that wing area. There are three definition about wing area: Trapezoidal, Wimpress (which is used by Boeing), and Airbus. But what is confirmed from that article is that the fuselage between the wing root in included as wing area regardless of whether it defined according to Trapezoidal, Wimpress, or Airbus' definition.

Typically, the reference wing area Sref, span b, and aspect ratio AR are based on somewhat simplified wing forms.  The reference wing extends to the aircraft centerline.
In the case of the aircraft shown, the reference wing probably matches what you've depicted -- with the exception of the 747.  For the 747, the reference wing likely excludes the trailing edge extension and any winglets.
Although these quantities are important for the aerodynamics and performance of the aircraft, they can also be somewhat ignored.
Imagine you have a wing with a very odd shape that is hard to deal with.  You could calculate a simplified reference wing with roughly equivalent Sref, b, AR.  As long as you always calculate the reference quantities the same way for odd shaped wings like this one, you'll be fine.

What is the definition of, or what do you mean with, Sref? Wing span and Aspect ratio of course no problem.

Sref is the wing reference area.  I don't really know why we use S for it, but that is convention in aerospace engineering.

S for surface? .

@AnonymousPhysicist I don't think so.  The surface area is a little more than 2x the reference area.  Really it is no more a mystery than why we use b for wingspan.

@RobMcDonald AFAIK S stands for "(projected) Surface area"

@AnonymousPhysicist, S is wing planform of the wing projected from top tangential to the earth. What I am asking here actually what is the meaning of the ref (referential), where it to be referred? Anyway, there is a good article or whatever you call it. https://leehamnews.com/2015/04/28/fundamentals-of-airliner-performance-part-7-the-wing/

@RobMcDonald, my concern is not about the S notation but about the ref (reference). Where does it to be referred?

b comes from Breite (width).

@AirCraftLover By reference, we mean that it is used in calculations, but it it might not exist on the aircraft at all.  We can use anything we want as Sref. Fundamentally, we use Sref when we turn aerodynamic forces into coefficients $C_L=L/(q,S_{ref})$. Later, we use Sref when we dimensionalize those coefficients back to forces. As long as we use the same Sref in both directions, we're OK.  When you see coefficient data for an aircraft or model printed, Sref should always be listed. For missiles and rockets, we use the base area of the largest circle of the stackup. It is just a convention.


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What changes are needed for a piston-prop aircraft to withstand saltwater environment?
I'm interested in WW2-era piston-prop aircraft. I want to know what changes are needed to make the aircraft withstand saltwater corrosion. Presumably these are different and more expensive than the normal land versions of aircraft, or they would make them that way in the first place.
I'm not interested in the usual carrier modifications, like tailhooks and wing-folding. For this question, I'm only interested in withstanding saltwater corrosion.
I have heard that aluminum resists saltwater corrosion very well. Not so sure about steel or wood. Are there differences in the air intake? What about certain delicate instruments like a pitot-static tube?
Edit: I was envisioning any combat aircraft that fight over the ocean, but especially the more exposed stuff like low-level torpedo bombers and seaplanes since they land directly on the water. Carrier aircraft is fine too.

thanks for the edit. the "are needed" phrasing made me thought that you were interested in doing them yourself, it looks like instead you are interested in what was done, right?

@Federico Doing them myself? No way, I'm not a mechanic or engineer. Not sure why I think in present tense for WW2 stuff so much but I guess it's because I try to put myself in that frame of reference. I was thinking of it in terms of an engineer at the time, or an engineering problem for that time.

I suspect that corrosion protection was not a major concern for WWII aircraft, as most were expected to be shot down or replaced by new generations long before corrosion would have an effect.

There is no way to fully protect an aircraft from the effects of salt water corrosion, even when any aluminium is treated with protection products like Alodyne. In fact, there is no way to prevent corrosion from happening anywhere unless you protect the item in question. Corrosion can affect an aircraft even in the dry climates.
Even if it is not landing or taking off in salt water, just being close to a body of salt water will cause corrosion. All you can do is be very proactive in washing the aircraft with clean water after every day, and using products like Corrosion-X to coat surfaces with a corrosion protection film. Even WD-40 will do a great job of this, because it is not a lubricant, it is designed as a hydrophobic [W]ater [D]isplacement product. You need to protect both exterior and interior areas, even inside the wings. Just ask any mech who has worked on aircraft for any length of time at a location near salt water.
Tailhooks and wing folding do nothing about corrosion, it just helps get the aircraft on the carrier and allows for efficient use of the deck areas.

When the first couple of Supermarine Spitfire fighters were deployed on a British aircraft carrier in the late 1930s, the structure was eaten away by corrosion within 6 months. The sea water spray was enough to cover them in salt, which would quickly reduce the aluminium structure to white dust. Before, Navy airplanes were of wooden construction, using steel for engines or bolts, but no high-strength aluminium.
During the Berlin airlift, table salt could not be transported by the usual fleet of C-47s and C-54s. Even the dust coming from the bags would cause rapid corrosion of the aircraft. So how did they bring the daily ration of 38 tons of table salt to Berlin?
Seaplanes can handle salt much better. Salt and baking powder was brought in by British Short Sunderland flying boats landing on a stretch of the Havel river inside West Berlin. Learning from the early experience with naval Spitfires, corrosion resistant alloys were developed. Typical for marine application are the aluminium-magnesium alloys that belong to the 5000 series. The magnesium oxides enhance and reinforce the protective oxide layer of aluminium whereas copper weakens the oxide layer. Early high-strength aluminium alloys use copper atoms dispersed through the aluminium matrix which locally distort the atomic lattice and strengthen it. This is called precipitation hardening, but is unfortunately exactly what makes the 2000 and 7000 series alloys very susceptible to salt corrosion.
So the answer is to pick the right alloy.
From this report on the subject:

Based on our very long experience of aluminium’s corrosion behaviour in marine atmospheres and in sea water, we can now assert that the service life of aluminium in marine environments will be exceptionally long and can be measured in decades!!! We can truly claim that aluminium is the “metal of the sea” of the modern age.

… but only when the right alloy is used!

While the 5000 and 6000 series alloys will be preferred for their resistance to corrosion, their weldability and their level of mechanical characteristics, other wrought alloys belonging to the 1000 and 3000 series are suitable for use in non-structural applications for decoration, interior fittings etc.
  The use of 2000 and 7000 series alloys on the other hand must be the exception in view of their poor resistance to corrosion, and they require special protection when used in a marine environment.

The best change you can make for an aircraft is a location change so its no longer near salt water...
On any note the most effective way to prevent corrosion of aluminum is to galvanize it. There are various galvanic paints and coatings that can be applied to your aircraft these are "cold methods". You can also do a true electrolytic method and hot dip it in zinc which is what Porsche did with the 70's/80's 911's to great effectiveness. A lot of modern planes use a zinc-phosphate primer to the same effect. Galvanizing an existing airframe may involve disassembling the majority of it.
Steel fittings and parts can be protected to an extend with things like WD-40 or a light coat of oil. The issue is this may involve you spraying stuff all over your airframe all the time which might not be great.
Where I live a hanger makes a big difference. It helps keep condensation off the plane which often comes in the form of salty air. Routine use and inspections to keep an eye out for corrosion and rust is a must.
Wood is a different story. With wood you get rot (and rust/corrosion on the bolts holding everything together). You can find more info on wood aircraft here broadly speaking wood aircraft are not as durable as metal for many reasons beyond rot.
Instruments need to be tended to like anything else, you need to watch for corrosion inside the pitot tubes as it can very well block or partially block it.
You may also find that electrical contacts corrode, dielectric grease is your friend and anything that seem intermittent should be checked right away.

Aluminum is prone to salt corrosion , with a small variation due to alloy. I believe all aircraft sheet metal is "alclad" . The surfaces have a thin layer of pure aluminum . It is anodic to the high strength alloy ( age = precipitation hardened) and protects it . Some shapes are anodized where a thicker oxide layer is electrolytically formed. And coatings are applied , likely the most effective protection . Landing gear ( very high strength steel) is another story ; It is subject to hydrogen stress cracking caused by wet salt corrosion - rust is not the problem. They were protected with cadmium plating and coatings ( but I am probably obsolete). There is a National Association Corrosion Engineers ( NACE) committee that deals with corrosion protection of military equipment ; they would have much more information.


text:
Is thermal expansion/contraction a major design problem for large subsonic airplanes?
Most large airplanes flying today are mostly metal, which has a relatively big coefficient of thermal expansion. Cruising altitudes of commercial jets can reach 10 km or more, where the air gets down to about -50 Celsius. Room temperature is more like +25 Celsius, and I would not be surprised if that large fuselage, sitting under the sun, gets up near +50 C.
This is quite a range of temperatures to handle. It would cause some contraction/expansion of metals. The larger the piece of metal, such as a wing spar or long airframe beam, the greater the contraction/expansion.
Is this a major design problem for large aircraft, and how is it handled?
EDIT: only interested in subsonic designs. I'm concerned about the cold high altitude air cooling most of the fuselage and making it contract. The nose and leading wing edges might not suffer from this, but I expect the rest of the aircraft will.

I won’t answer because this is an anecdotal story, but I once had a gripe that every time this specific aircraft (an Airbus as it happened) ascended through 18,000 feet, a spurious warning light would go off in the cockpit. Long story short, we had a real bear of a time finding it because it operated fine on the ground. Turns out that a wire was chaffing to structure because a clamp was turned the wrong way. The thing is that the structure would shrink so much in flight that it would cause this friction but on the ground the fuselage would expand enough so that it didn’t rub, and worked fine.

@Frank Uh oh, what kinda warning light? Was it something serious like thrust-reverser unlocked?

I don’t remember which light, exactly. I remember it wasn’t anything that would jeopardize the aircraft, but it had a very lengthy history of intermittent behavior. Naturally, it always worked fine on the ground. By the way, the distance between the clamp and the fuselage on the ground was several inches, which is partly why it was glossed over during inspection. No one thought that there would be that much contraction!

Not thermal contraction but condensation of vapor is a problem.
Immediately, fuselage pressurization is the far bigger problem that comes with the altitude changes. But if you operate in hot and moist weather, the moisture in all the air carried inside the fuselage will condense when this air cools down at altitude and will collect somewhere. If no proper drains are included (remember, drain valves and fuselage pressurization do not mix well) and maintenance is sloppy, this accumulated water can weigh several tons.
A special case are foam sandwich structures. PVC foam is the standard in composite gliders, but airliners use honeycomb sandwich structures. When fairings made from PVC foam were tried on airliners, it was found that pressure and temperature cycles damaged the sandwich core pretty quickly. The moisture inside the cells would condense, the cells themselves would crack and bacteria would munch up the soggy remains. Only with honeycomb cores could the sandwich be made durable enough for airliner use.

The temperature range the aicraft is dealing with is actually smaller. Indeed, airliners cruise around Mach 0.85, but the velocity on the fuselage is zero. Hence a part of air kinetic energy is transfered into thermal energy. This is called the ram effect. You can find tables that give you the stagnation temperature as a function of the mach number and the altitude.

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text:
Why hasn't there ever been a large 4-engine commercial airplane with 2 engines on the wings and 2 engines at the tail?
This question refers to large passenger jet aircraft only, which I define as being able to carry at least 100 people.
There have been many 2-, 3-, and 4-engined planes in this category. Some of the twinjets have both engines on the wings. Other twinjets have them both at the tail. Some trijets have all engines at the tail, and other trijets have 2 on the wings and 1 at the tail.
But most quadjets (again, only 100+ passenger jet airplanes) put all of them on the wings. Why not put 2 on the wings and 2 at the tail?
Such a configuration would save weight on the wings, because the wings wouldn't need to be so strong to support 2 outboard engines far away from the fuselage. If twinjets can be configured with both engines at the tail, then I see no reason why a quadjet cannot.
In fact, I know of one old quadjet that put all engines at the tail---the Ilyushin Il-62. So I do not think balancing the center of mass and center of pressure is a problem. Some trijets put all engines at the tail, whereas what I'm talking about would only put 2 engines at the tail (and 2 on the wings).
So is this a good idea? Why not do it this way?
EDIT: It was pointed out that exhaust from the wing engines would interfere with the rear engines. If so, then can't we borrow the trijet design for the intake? A large intake at the vertical stabilizer splits in half and feeds both rear engines.

@ymb1 Interesting, but if trijets can do it then i don't see why quadjets cannot. For the complex fuel routing, I opened a separate question about it for trijets: http://aviation.stackexchange.com/questions/31522/how-is-fuel-stored-routed-on-a-trijet-with-1-engine-at-the-tail

@ymb1 btw, what is "hyd"? I'm skeptical of your comment because trijets already exist. The single rear engine may not even need a generator or bleed air (for cabin purposes) anyway. Both of those can be handled by the 2 jets on the wings. But exhaust disturbing air at the rear engines, yes, I can see that.

Related

Other quadjets: Lockheed Jetstar L-1329 aircraft

Don't forget the VC10

"the wings wouldn't need to be so strong to support 2 outboard engines far away from the fuselage" -- is that really true? On the ground, it is true that wing-mounted engines must be carried by the wing spars, but in flight having the engine on the wing places it right where the lift to keep it up is generated and right where the thrust needs to apply to counter the induced drag. WIth a fuselage-mounted engine these forces need to be transmitted to the wings in flight.

@HenningMakholm Of course on the ground is a different load relation than in flight, but the wing has to be engineered for both. Otherwise the wing would break off on the ground!

@DrZ214, the aircraft must survive at least -1G to +2.5G in flight and that always means higher loads than those on the ground.

Possible duplicate of How does the mounting location of a jet engine affect aircraft performance?

@cavver and the Trident 3B which added a small booster engine for a total of 4 (one either side of the tail, and 2 embedded)

Or, to stretch a point until it almost breaks, Concorde, where all 4 engines were under the wing, but at the tail, because of the delta wing

Such a configuration would save weight on the wings, because the wings wouldn't need to be so strong to support 2 outboard engines far away from the fuselage.

You seem to be under the impression that the fuselage supports the wings. The reality is the other way around (in flight, at least.) The wings are the most efficient place to hang weight, as they are what is providing most of the lift. This is why the main fuel tanks are usually located in the wings, for example. The strength required to support an outboard engine while the plane is sitting on the ground should be relatively small compared to the strength required for the wings to support the weight of the entire fuselage (including your proposed tail-mounted engines.) Aircraft with tail mounted engines actually need a heavier wing spar, not a lighter one.
It's also important to note that aircraft with 4 engines nowadays are usually very large aircraft with very large engines, such as the 747-8 and A380. Engines of this size would be very difficult to mount from the tail, especially with the modern high-bypass turbofans and their enormous diameters. Think of a GEnx with 2.8 m / 111 inch diameter fan, for example. This would require strengthening the fuselage as well as the wing spars and would also wreak havoc on the center of gravity. Having twin tail-mounted engines would also probably require converting the plane into a T-tail, which causes yet more engineering problems for an aircraft that large. The bending moments on the engine mounts would be enormous, too.
Can you imagine this hanging from the side of the fuselage? Note the size of the engine compared to the size of the van parked beside it.

GEnx hanging from a 787 wing Source: Wikipedia
It is usually only much smaller aircraft that have had tail-mounted engines. This is done largely to allow them to keep the wings low to the ground. For larger aircraft, there's usually already enough clearance under the wing to mount the engines anyway or, at least, the increase in wing clearance needed to wing-mount the engines is not as much as would be needed in a smaller aircraft. Of course, for high-wing airplanes, clearance is also not an issue and most of these do indeed wing-mount the engines, even on small regional jets. For example, the Avro RJ-100:

SWISS Avro RJ-100 with wing-mounted engines Source: Wikipedia
The question Why do large aircraft have their engines mostly on the wings, while smaller ones tend to have them in the tail or the tip? provides more detail on this. As usual, Peter's answer is informative and there are other good answers, too.

You seem to be under the impression that the fuselage supports the wings. The reality is the other way around (in flight, at least.) I know the wings support the fuselage in flight, and the fuselage supports the wings on the ground. I know the load relations are reversed. But you have to engineer for both, don't you? Otherwise the wing would snap off on the ground! Putting engine weight farther out places higher torque on the wing and also doubles the length of the strong spar, adding weight.

@DrZ214, yes, for both, but the loads in flight are far greater than those on the ground. The wing must support the whole structure (including engines when mounted on the fuselage), all times the maximum load and safety factor (~ x3). It is a well known basic fact in airplanes engineering that wing-mounted engines save weight. There are (military) designs where engines (or fuel tanks) are even placed at the wing tips.

@DrZ214 Yes, you need to engineer for both, but the fuselage usually weighs more than the wings already and you don't have to deal with sudden changes in the forces due to turbulence when you're parked on the ramp vs. when you're flying through a jet stream. Gravity doesn't tend to fluctuate much on the ramp, whereas lift can fluctuate substantially in flight as a result of turbulent airflow (or AoA change in general.) The spar already has to be long in order to use the lift from the outer part of the wing without snapping it off in flight.

Otherwise the wing would snap off on the ground!  -- that would only happen in a plane where the wing is significantly heavier than the fuselage. Any wing that would snap off on the ground would definitely snap off in flight.

reirab provided a good answer, and I'd just like to summarise it in simple terms.
The essence is: such configuration has all the disadvantages and very few benefits compared to the traditional design (or all-tail design for that matter). It also adds its own problems like exhaust interference mentioned by ymb1.
If you have two inboard engines under the wing, you already must provide enough ground clearance for them (with the associated drawbacks of heavier landing gear, maintenance etc.) What's the point of having the other two engines at the back then? It will substantially complicate the fuel system, CG/load management, and, as explained before, will add weight.
This weight penalty comes not only from the unfavourable load distribution, but also because wing-mounted engines work as anti-flutter weights (this is why they are protruding forward rather than being just under the wing). The Ilyushin Il-62 you mentioned has heavy steel weights all along its leading edge.
When you have all engines at the back, at least you can benefit from the 'aerodynamically clean' wing and low ground clearance. For trijets, you'd want to mount the 2nd engine symmetrically, so tail is the only reasonable option - otherwise designers would happily hang it on the wing. (That said, I remember reading that DC-10 (or L-1011?) designers considered mounting the tail engine on one side of the fuselage).

Having the engines in front of, rather than under, the wing also lets you get away with mounting them higher up than would otherwise be possible; Boeing took advantage of this when they were reengining the 737 in the early 1980s.

Like the answer posted above, the hot air from the front engines would decrease the efficiency of the rear engines. I think it could probably help balance out the weight, but it would be too complex and too innefficient. (this might just be me, but the throttles would be confusing. most planes have left->right as 1->whatever. with this design, there would be more difficult things.) overall, just too many small issues from solving one problem (if weight distribution is really that bad)

also, you can see one of these on google earth. perth airport, (31.56'47"S, 115.58'12" E). just a little malfunction

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How long to clear the 'suck zone' of a turbofan after start is initiated?

I recently found this (IMO funny) picture. All funny and all. But let's make this a real situation.
Let's suppose I see my crush and his BF doing this, and I come with this 'genius' idea (alright, it's anything but a genius idea, but still) to start the engine they are sitting on. And no, I am not nice enough to turn the beacon lights on.
How likely is it that the engine gains enough suction to suck them in without they noticing it in time (considering the fact they need to standup and run for their lives)?
How long does it take for the engine to spool up enough suck a person in?

I'm not sure why the VtC for "opinion based". Seems that there are some pretty reliable facts already posted in the answers.

Since they are both wearing ties, one would hope that'd get sucked into the core.

Ironically, that looks like an A320, but the start panel is from a B737.

That picture's totally inappropriate for this site. Who starts engine 1 first!?

Not trying to misgender anyone here, but, considering that the people in the picture appear to most likely be a guy and a girl, it'd probably be "...and his GF" or "and her BF". ;-P

A start on a TF all the way to idle is about 20-40 seconds depending on the engine, and the fan itself won't do more than creep a bit until the core actually lights off which is 5-10 seconds, so they'll have lots of time to get down and get away as per @ymb1's diagram, once the wheeEEEEEEEEEEtickticktickticktickticktick starts.

I love the written description of the startup sound. +1

From now on this is the sound of evil.

@Peter It's music.  Best of all is the sound of a Huey helicopter. https://www.youtube.com/watch?v=IA9knzev85I  Listen carefully. There must be 4 or 5 ascending howls and groans and whines in a sequence as the, starter, engine and various gearboxes wind up in turn.  It's a symphony.

Hmm... How much suction is the core creating during that 20-40 seconds, though? N2 has to get relatively high before the core lights, doesn't it? Seems like that would still result in a pretty substantial mass flow (though obviously not as much as when the fan spins up.)

WHAT??? I CAN'T HEAR YOU
I said, let's get away from this loud engine!
Before it can even start to turn the fan, the noises the engine must make will be so deafening as to force the people in that location to flee.
And even before that, there would be clunks, shakes, and vibration that would be very noticeable, and put even deaf people on notice to clear out.
There would be no mistaking the engine starting up. They would have at least 10-15 seconds to clear out.

This doesn't actually answer the question. Q: "How long?" A: "Well they'll definitely hear it!"

@Clonkex it's implicit that it gets noisy enough, early enough that they would move away because of the noise before they would get sucked in.

Obviously each engine takes a different amount of time to start. The point is that you would always notice it starting up.

@Baldrickk Yeah I know, but generally it's expected that Stack Exchange questions should directly answer the question. I'm just suggesting perhaps the author should edit the answer to make it a more direct answer. And of course... I have a cunning plan...

@Clonkex ok, there ya go!  It's a hard question to answer so I had to couch it...


text:
Was the B727's wing supercritical (even if not so designed)?
The Boeing 727's wing upper surface appears unusually flat, especially at the root (Albeit at an angle).  Refer to the images linked below:

airlinereporter.com

Flickr

Also from Flickr

Was the B727's wing designed as supercritical? Did the B727's wing behave in a supercritical fashion, even if it wasn't explicitly designed as such?

Also notice the difference in AOA between wing and horizontal stabilizer in first picture!  Keep in mind they probably did not need a lot of airfoil lift at cruise, and would reconfigure for landing, so one may not see a "classic" airfoil shape here.

I've got an aged book on pre-design of aircraft, which states that the B727 wing thickness was 13% at root and 9% at tip, average thickness 11% chord. $M_{M0}$ = 0.9, first flight of prototype is noted as 1963.
The 727 was a derivative of the 707: first flight 1957, average thickness 10% chord, $M_{M0}$ = 0.9. So the 707 wing was even thinner than B727, Mach number is the same. Profile of both airliners is not listed as a NACA profile.
The book references the first research paper on supercritical profiles as T.G. Ayers: Supercritical Aerodynamics Worthwhile Over A Range Of Speeds, published in 1972, nine years after the B727 prototype flew. The profiles depicted in the report seem to be thicker than those of the B727.
The photos in the question focus on the wing root, however the shape of the wing root is not indicative of that of the rest of the wing, but determined by a lot of structural and aerodynamic factors: placing of landing gear, fairings for aerodynamic interference etc. Furthermore, the overwing exit is there and evacuation of passengers should not be too difficult, caused for instance by a bulgy shaped cross section. It would make sense if this bit of the wing was designed mainly with evacuation in mind.
So it appears from the published date of the research work on Supercritical wing design, and from the similarity with the much older B707: no, the B727 did not have supercritical wing profiles.
Update
The main advantage of a supercritical wing is that it enables reducing the wing sweep. There was some progress between 707 and 727, because wing sweep was reduced from 35º to 32º on the 727. However, the A320 has a comparable $M_{M0}$ and has wing sweep of 25º. So again without knowing what exact wing profile was used and based on order-of-magnitude checks, it does not look like the 727 had supercritical wing profiles.
The profiles of supercritical wings I've seen are flat on top indeed, and horizontal and thickish and have a characteristic curve at the end. Flatness per se does not indicate that the profile is supercritical, for example NACA 23015 isn't.

 The horizontal flat bit on top allows the supersonic area to expand calmly again, but it needs to be horizontal, like indicated in this figure from E. Torenbeek, Synthesis Of Subsonic Airplane Design:

Update 2
A fascinating film explaining how high subsonic speed was achieved before supercritical rear loading profiles were implemented on aircraft. Discoveries like these are what I love about the Aviation SE site. From this question & answer

The characteristic curve at the end is called rear loading and contributes most of the lift at maximum Mach. By the way, the first work on supercritical airfoils is from 1940 by Kawalki and the first airliner to use a supercritical airfoil is the Vickers VC10; however, at those times the airfoils were not called supercritical.

The 727 wing is a derivative of the earlier Boeing 720 wing which incorporated the leading edge glove, an added feature ahead of and atop the old airfoil from the fuselage to the inboard engine pylon. Actually that leading edge glove is a copy of the old original wing airfoil instead of designing a new one that would have been more costly. The 727 wing used that extended leading edge idea and incorporated that concept in the wing box structure, which actually creates a double sweepback wing plan form into the wing design directly rather than add it on as it was in the B720 and also on the 707-120B as well. That saves weight also. The inboard leading edge radius actually is tilted up above the reference or wing chord plane and in doing so makes the top of the wing contour more flat as that contour is twisted and becomes flatter than had it been done without that up tilt. The purpose of this up angle is to add lift to that part of the wing which had it not been done otherwise, would lessen the lift in that inboard part of the wing, which had also been done in the glove add-on the 707 and 720 attachment mentioned earlier. Without it, the wing thickness chord ratio would be thinner there at the fuselage and lift would have been compromised as such. With a normally placed leading edge radius on the wing chord plane, the top of the wing would be more rounded. The redesigned wing leading edge radius eventually becomes normal outboard where the double sweep back ends and the wing upper surface becomes more rounded at the wing chord plane.


text:
What is the trend of gender distribution among pilots?
Are there any statistics on the distribution of pilots between the two genders? Specifically, has the ratio changed over the past decades (I'd expect female pilots to be getting more common)?
I'm aware that the number will vary between countries. I'm more interested in the trend of certain group(s) that are statistically significant to an area (e.g. all commercial carriers in the United Kingdom / all PPL holders in the United States).

Edited wordings. I'm just curious to know the general trend over, say the past 30 years.

I assume you're not asking for countries were women are not allowed to drive a car.

At least for the FAA, you can get the U.S. Civil Airmen Statistics as a download that covers from 2005 to 2014. It includes data based on gender and license type. I'm not sure when they will update for 2015. If you download the 2010 one, it has data back to 2001, so about 13 years of data.
Here is an example of the data provided:

Similarly for the UK, you can download statistics from this website. I haven't downloaded them but it looks like what you are looking for is there.
You may be able to find similar data for Canada, Australia, and some other relatively "open" countries.

This makes me want to know more about that one last flight navigator holdout.

Air Canada's pilots are about 95% male and that is about average for all North American airlines.   The Air Line Pilots Association, which represents pilots in Canada and the U.S., recently reported that 5.4 per cent of members are women. British Airways said in 2013 that 200 of its 3,500 pilots are women – about 5.7 per cent.
Air Canada's first female pilot was hired in 1978 and recently retired after 37 years.  Air Canada's first female pilot retires, 95 per cent are still men

Why is this?....


text:
Are air traffic controllers required to obtain a pilot license?
Here in my home country (Hong Kong), all air traffic controllers are required  to obtain a PPL as part of their training. The reason being, if the controllers can better imagine a pilot's perspective, they can better accommodate and provide assistance to pilots. I don't think they are required to keep the license current, but sure they need to pass all PPL exams.
Is this requirement common around the world? (Note that I intentionally do not specify which country or jurisdiction. I'm looking for an answer which lists the countries which have this requirement.)

No requirement in the UK and I'm sorry, I am going to vote to close since this question could have 178 answers of "not in xxx country".  Perhaps you could reword it to say please only answer or comment if the answer is "yes".

@Simon instead of 178 answers, perhaps an answer would say "Except for Country A, B & C, the US, Australia and all other European countries do not have this".

@kevin I'm not trying to be confrontational, but I can't actually find any 'evidence' that Honk Kong air traffic controllers obtain (or are required to) a Private Pilots License as part of their training. Can you cite some references for that as it does appear to be a very unusual requirement and well beyond ICAO

Interesting, I can indeed find quite a few references to flying training as part of becoming a controller (Though I can't confirm whether they have to graduate as a pilot). It's an interesting one - I can certainly understand "seeing the other side", but I question how much of a crossover between having a good aptitude for flying vs being a good controller there really is. (NB: I'm sure many do both extremely well, I'm just not convinced that there's a real correlation)

@Dan http://www.cad.gov.hk/english/atm_training.html . Training takes around a year, during which 3 months are spent overseas to obtain a PPL, usually Australia or New Zealand.

@kevin Thanks Kevin - I don't want to go too far off the point of your question, but it has sparked my interest. It's this line I can't quite fathom - ' "As part of the air traffic control training, SATCO have the opportunity to take up overseas flying training in single-engine light aircraft." which doesn't imply it's a mandatory requirement, but that might be just the wording.

In the US, controllers are required to do some ground and flight training (at least in some training tracks), but there is no requirement to complete that training by earning a pilot certificate.

I find it unbelievable that controllers in China have pilot's license. It very difficult and expensive to fly in China and they have a severe shortage of pilots. Until 2013 it was extremely difficult to even fly at all because of the need to obtain permissions weeks in advance for each and every flight. If a controller had a license, why would he even work as a controller when he could make much more money as a pilot? The statement in the question just isn't believable.

No, there is no such requirement here in Germany.


text:
Can you help identify this vintage aircraft?

Please help identify this aircraft. Photo taken in Rijeka, Croatia early 1900s

This is a Dornier Do D, a floatplane torpedo bomber variant of the Dornier Komet, which was built for the Yugoslav Royal Navy. It's considerably bigger than it looks in your picture!
203 served with the Yugoslavian 20th Hydrosquadron from 1927, originally based in Kumbor, Montenegro. In this early variant, the pilot sat in the forward cockpit, right under the wing - you can just see him in the second picture - a bold design feature. Later variants rearranged the fuselage and cockpit. Here is the exact same plane -
 source
 source

source

Outstanding answer!

Wow.  Thank you for the information.  That is way more than I was expecting.  -Chris

@ChrisVolker That is way more than I was expecting - so show your delight by accepting the question  (checkmark under the votes at the left of the answer, turns green when checked)


text:
How did night fighter aircraft manage to shoot down their foes in World War II?
I know that those plane had radar to acquire an approximate location of the enemy, but how did they spot them after that? You need to be accurate when you try to shoot down an enemy plane, and deflection can be tricky, even at close range. So how did pilots aim in those conditions?

One word: Skill.

https://en.wikipedia.org/wiki/Night_fighter

Ok, the use of "no" was probably too strong - "few" would have been better. But I still don't get what radar has to do with shooting down foes in WWII.

Those antenna are not the antenna of radar ? Even the P61 had a quite modern one

I mean shooting enemy plane. They had spotlight to search for enemy bombers but not always. BVR dogfight did not exist, so my question was about the tools that were used to help pilots  locating enemy planes at night, since he could not see them.

@Jamiec: Judging by the answer so far, it more sounds like the word should be "badly" :-D

The antennae sticking out of the nose of WW2 night fighters are radar. That's what many early aircraft radars looked like.

Short answer; luck. Answers focus on WW2, rightfully so. Gun attacks were all that was available and a British bomber stream could not be unopposed. However the cost / reward was disproportionate.

@user19759  Actually there were HVAR aerial rockets in WW2, though mainly for anti-bomber operations.

The night fighting in WWII was mainly between the RAF and Luftwaffe, with the Luftwaffe fielding most of the night fighters due to necessity (the others too had some fine night fighters, though none had their need as much as the Germans).
The first stage in (trying to) shoot down enemy aircraft is to find them. This was mainly done by the ground based radars. The second one is fixing them- this is where the aircraft based radars came into being.
Initially, the fixing of aircraft location was done using ground based search lights, which were sometimes controlled by radar after which the fighters attacked the illuminated target- but this was of little use as was the aircraft based searchlights. It was only in the middle of the war did the development of night fighters gained pace.

A Messerschmidt  Bf 110 G-4 night fighter with FuG 202/220 Lichtenstein radar; By Max Smith - Own workMoved from en:Image:ME-110G-2_at_RAF_Hendon.jpg, Public Domain, Link
The night fighters were usually twin engined aircraft fitted with radars, though there some single engined ones too. The fighters were still vectored into the bomber locations using the ground radar controller. An RAF report on PoW interrogation notes:

...The crews fly by D.R., and the loose formation is simultaneously tracked on a map at Gruppe headquarters. If, in the light of the movements of the bomber force a change of course is necessary, a new bearing will be given to all aircraft simultaneously through the Gruppe commentary.
All crews are given strict orders to navigate by D.R., and to
accept the Gruppe orders if these differ from their own calculations ...

Once the fighters were near the bomber stream (as the RAF usually bombed in strength to overwhelm the defences), they were given a new bearing to intercept the bombers.

... the string of night fighters should be brought up to the bomber stream on a parallel or nearly parallel track. At the correct moment, and in accordance with D.R. tracking at headquarters, the night fighters will be given a new bearing which turns the whole line on to the bomber stream in a broadside.

The enemy aircraft (bombers) were identified by their silhouette (against moon or the burning cities below) or by their exhaust flames.

Recognition of the target aircraft is usually by the silhouette in light conditions or moonlight, and by the four exhaust flames in darkness.

The actual firing of the guns depended on the pilot and different ones opted for different methods- some simply did as in dogfights during day- get into the rear and shoot up, though the rear gunners made this difficult. Others moved towards the aircraft from the sides and a little low, after which they pulled up near the aircraft and aimed for the wing fuel tanks.

The range at which the night fighter opens fire with its forward
armament is determined by the pilot himself; whilst some will close in
as near as 50/60 metres, the more cautious will open up at a range of
200/250 metres. P/W considered, however, that the normal range might be
taken as l00/150 metres.

One of the effective methods used by Germans was the upward firing cannon called the Schräge Musik, which was quite effective with its 20 and 30 mm cannon.

By Source, Fair use, Link
Basically, the pilots flew under the bomber and fired the Schräge Musik. This was quite effective as the bomber crews had little warning of the threat below and the bullets usually tore through the fuel tanks near wing roots.

[These P/W] ... they stated that once this armament (Schräge
Musik) could be brought to bear it was extremely effective; one officer had claimed a kill with two rounds from the 20 mm. cannon.

The night attacks were quite short affairs as it was quite difficult to keep the bomber in crosshairs for any amount of time (and there were enemy night fighters to contend with). Shooting down enemy aircraft took more luck than skill in WWII. According to this site, each enemy aircraft shot down required more than 10,000 rounds fired (the values are more or less equal for both sides), with night attacks probably requiring more ammunition. Also, this infographic has some good details on this subject.

There are so many inaccuracies and omissions in @aeroalias' answer that I take it upon myself to add another answer.
Early Years (1939 - 41)
Up until the start of the war, aircraft were located by listening stations. By feeding each ear with a super-sized, moveable ear trumpet, both direction and elevation of an approaching aircraft could be determined by a trained observer. Another method were large, spherical concrete mirrors with a moveable microphone placed in front of them.

Soldiers operating an acoustic airplane locator during World War 2, Trelleborg, Sweden, 1940 (Picture by Carl Gunnar Rosborn, source)
This could only provide an early warning and an approximate location which was then radioed to the fighter aircraft. Those had to rely on their eyes to find and attack the aircraft, which was relatively easy in moonlight. The hard part was to navigate back to the airfield.
When the war started, Britain had nearly completed its Chain Home early radar installation while Germany had just fielded eight of the more advanced Freya stations. Both could detect aircraft at greater distances and accuracy than listening stations and Freya even provided early friend-or-foe capabilities with properly equipped aircraft. While the Chain Home system relied on direction and speed to distinguish between friendly and hostile aircraft, Freya stations (which were later completed with Würzburg stations for height finding) could already direct individual fighters to their targets. Tracking was manual and detection errors frequent.
The fighters were regular single- or twin engined aircraft and initially their only modification was a black coat of paint as camouflage. On both sides, otherwise obsolete designs were used successfully as night fighters. On the British side, a few like the Boulton Paul Defiant were designed from the outset to fend off intruding bombers, day and night.

Low-level aerial reconnaissance photograph of the Freya radar installations at Auderville, France, 1940 (picture source)
Since bombing raids by the RAF on civilian targets started already before the end of the "phoney war", I will focus on Luftwaffe tactics:

Dunkle Nachtjagdt ("dark night hunt") The fighters assembled over a radio beacon and were individually led to their targets via radio commands coming from a Freya station. At close range visual identification was used to target and shoot.
Helle Nachtjagdt ("light night hunt") Here a trio of searchlights was slaved to one Würzburg station and a second Würzburg was used to track and direct the fighter while the Freya was used for long-range detection. When the three light beams converged on their target, the fighter could use this illumination for the final approach and targeting. Due to the scarcity and immobility of searchlights this technique only worked when the bomber track was close to the searchlight stations. This worked best with little or no cloud cover, but bomber navigation also required cloudless skies, so this technique worked well initially.

Intermediate Years (1942 - 43)
A big improvement in accuracy was the addition of lobe switching to the radar systems. A rotating, slightly offset receiver in the focal point of the Würzburg antenna produced a spherical scan, and the operator could compare the returns of the radar blips to direct the antenna in the direction of the aircraft. If all returns were of equal height on the oscilloscope screen, the antenna pointed directly at the aircraft. Next, a hierarchy of command stations was built up to collect the information from all radar sites and direct the fighters centrally. Larger and more powerful systems were deployed with better accuracy and range. Also, the display of aircraft locations was refined: The command stations had plotting tables (Seeburg-Tisch) with a map on which the aircraft were displayed as light dots, so the Jägerleitoffizier (fighter command officer) could better direct the fighter.
Countermeasures were the focusing of the bomber stream on a narrow range of the belt of radar stations and searchlights (Helle Riegel) from 1942 on, so they were simply overwhelmed. Remember, three radar stations were needed to direct one fighter to one target. In 1943, the RAF added the dropping of clouds of strips of metal foil (Window), the length of which was tuned to the radar wavelength, thus over-saturating the radar returns. As a response, the rigid system of a single line of defence (Kammhuber line) was broken up into a number of stations around possible targets for in-depth defense, and fighter aircraft were equipped with their own radar system to give them more independence. British Bristol Blenheims and Beaufighters had early onboard radar systems installed as early as 1940, their development prompted by the low accuracy of the Chain Home system. Also, airplane-mounted infrared searchlights and infrared receivers were tried out but were found to be lacking.
The Seeburg-Lichtenstein-Verfahren, called after the plotting table and airborne radar, still needed long range detection by ground based radars. In that, it was helle Nachtjagdt without searchlights. By adding simple direction and range finding ground equipment for directing the actively radiating fighters, the Y-Verfahren could switch all radars to the tracking of bombers, thus doubling the number of intercepts which could be managed by one Himmelbett station (a ground station with added fighter tracking equipment). However, now the fighters would give away their position also to the enemy, and specially equipped RAF fighters could home in on the radio signals of the Luftwaffe fighters.

Radio operator instruments in a Me-110 G-4 (picture source)
Late Years (1944 - 45)
A steady stream of improvements saw a move to higher frequencies (to reduce antenna drag) and variable frequencies (to tune away from chaff), but the general tactic of centrally directing fighters into a larger area and leading them near their targets with large, ground-based radars was maintained until the end of the war. By using PPI displays, those radars could cut through chaff and became effective again in directing fighters, because the detection range of their onboard radars was still limited. Both sides used the emission of aircraft-mounted radars to home in on the enemy, using passive detectors.
When the number of allied aircraft overwhelmed the limited number of dedicated night fighters, regular day fighters were used in parallel in increasingly desperate ways. After General Kammhuber was replaced in his position as head of night fighters by the much more aggressive Hajo Herrmann, new tactics were developed:

Zahme Sau (tame sow) saw the use of FW-190 and Me-109 (Herrmann himself flew at times an aircraft carrier variant of the 109 E which was outdated for daytime use in 1944, but fine for night fighting) aided by illumination from flares dropped by high-flying Ju-88s. Later addition of passive receivers aided greatly in leading them to their targets, and without active radiation sources they were immune against countermeasures. Also, the radars would now multi-task, leading several fighters in short sequence to their targets. This way, a single Himmelbett installation could direct 15 fighters.
Wilde Sau (wild sow) While Zahme Sau kept reserved areas for ground-based anti-aircraft fire, Wilde Sau extended the concept to mix AA and night fighters. By staying above the altitude at which AA grenades would explode intro shrapnel, the fighters were supposed to avoid being hit by friendly fire, and the FlAK searchlights helped in navigating to the bomber stream and picking up targets (most effective when shining against a lower cloud layer). Again the problem shifted to finding home after an attack, and elaborate radio navigation aids and ground illumination was used to help the fighters find home.

This is a far more comprehensive and accurate answer than the other one currently. It talks a ton more about how the back and forth went between British/German technology, which was a big piece of this question - particularly Window, which illustrates how effective radar was prior to its deployment.


text:
What is the difference between RFL and ECL in Air Traffic Control?
There are two messages to change the Flight Level: RFL and ECL. However, I don't know the differences. Can anyone explain them?

RFL is Requested Flight Level, ECL is the En-Route Cruise Level. RFL the cruising flight level that has been requested by the flight plan or by the pilots, ECL is the level which has been actually assigned by the controller. The two may be the same or they may be different.
From the EUROCONTROL SPECIFICATION FOR TRAJECTORY PREDICTION Edition: 1.0, page 33

2.3.2  Enroute Cruising Level (ECL) (3.3.2)
Domain Knowledge: The  ECL   is  a  notional
  level  that,  in  the  absence  of  constraints,  equates  to  the
  RFL .  In  the  case  where  a  flight  is  not  permitted  to  cruise
  at  its  RFL   for  any  or  a  part  of  its  route,  due  to  the
  presence of a  strategic constraint (level limit) which applies to
  flights between the  aerodromes of  departure and destination, the ECL
  will be limited  to the level defined by the constraint. The ECL may
  also  be  changed  by  instruction from  ATC where  the flight is to
  maintain a different cruising  level, typically due to the proximity
  of a flight at the  RFL  on the same  route.   As with the  RFL ,
  the  ECL  can be changed for different  segments  of the  route  and,
  if different in  the  cruise  phase,  is  changed  to  the  XFL   on
  passing  the  sector   boundary.  The  notion  of  ECL ceases to exist
  after the final  TOD  from cruising level.

This is a complicated way of saying the requested flight level is usually assigned unless there's a good reason for the controller not to (to avoid potential conflicts for example), and the pilots can request a different flight level en route.


text:
How does the shift in aerodynamic center affect the performance of swing wing aircraft?
I am trying to understand how a  variable sweep wing changes the aerodynamic center of a plane, and its effect on the plane's maneuverability. I also would like to know the importance of the pivot point as it somehow affects the center of pressure.

Possible duplicate of Why do some military aircraft use variable-sweep wings?

Not duplicate, why swing wings are used is not same as how their use changes the Center of Pressure.

With so many questions I need to structure the answer:
Effect on performance
Moving the wing backwards will also move the aerodynamic center backwards, but the high sweep of a swing wing normally means that the wing's leading edge is still subsonic even at Mach 2. This means that the aerodynamic center of the wing ist still near the quarter chord, so the shift in the center of pressure is limited to the geometric shift from sweeping the wing. Generally, a swing wing needs to be combined with a generously sized horizontal tail to have enough trim authority for all sweep angles.
The first jet capable to change sweep angle in flight, the Bell X-5, therefore shifted the wing forward when sweep was increased. Later designs used fixed pivot points, however.
If no possibility exists to trim the aircraft by shifting weight (mostly fuel), swing wings cause high trim drag when swept back. The biggest source of drag, however, is the increased structural mass for the sweep mechanism which will cause an increase in induced drag. Further, the mechanism takes up valuable volume at the center of the aircraft which now cannot be used for fuel storage. In total, the substantial improvement in wing drag due to variable sweep is almost completely eaten up by the mass increase and the trim drag increase.
A clear benefit of variable sweep is improved low speed performance: Both the reduced sweep and the increase in wing span will reduce low speed drag substantially, so a swing-wring design will show superior loiter performance. Also, take-off and landing distances are reduced because the full wing span can be used for highly effective slotted flaps.
Effect on Maneuverability
Swing wings cannot have ailerons - the high sweep angle of the trailing edge at high speed flight makes control surfaces there almost useless. Therefore, a swing wing aircraft will use differential deflection on the horizontal tail in lieu of ailerons (tailerons). At low speed this reduces the possible roll rate -- the unswept wing contributes high roll damping while the tailerons will have limited effectivity due to their small lever arm. The F-14 uses wing spoilers to improve roll rate at lower sweep angles, but spoiler control is less efficient than ailerons.
At high speed (and sweep angles) the reduced aspect ratio, the increased sweep angle and the much reduced moment of inertia around the roll axis will combine to produce a very agile aircraft.
Pivot position
The further outboard the pivot point, the smaller the shift in the center of pressure. If the wing uses a highly swept root, the pivot can be positioned outboard without loss of efficiency at high speed. Examples are the Sukhoi 17 or the Tupolev Tu-22. An outside pivot position also allows to place external loads on the inner part of the wing (wing glove) and to avoid the complexity of moveable wing stations.
The Grumman F-14 also extends a small, triangular wing extension (glove vane) at the leading edge when the wing is swept back to reduce center of pressure travel. This feature, however, was disabled later to reduce weight and complexity.
The reduced top speed demands on modern fighters mean that variable sweep will no longer be attractive to achieve an optimum design. Variable sweep vanished with the Mach 2+ requirement in the 1980s.

Check out this discussion, or this one
from which I quote:

NASA conducted a large research program on swing-wing aircraft design.
  One design alternative that NASA developed was used the F-111 as well
  as in later aircraft, such as the F-14. Instead of placing the pivot
  point for the wings in the center of the fuselage, each wing was give
  its own pivot point, and the pivot point was placed several feet
  outboard of the fuselage. The pivot points were covered with an
  aerodynamic fairing and became part of the wing. This arrangement
  effectively divided each wing into two parts—a nonmoving wing glove
  section covering the wing pivot mechanism and a swinging section. As
  the swinging section swept back at higher speeds, it would lose
  aerodynamic effect. However, the wing glove section would increase its
  aerodynamic effect as speed increased. This lessened the shift in the
  center of pressure.


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Why not increase the number of Flight Data Recorders and add jettisoning capability?
With some Flight Data Recorders gone unrecoverable during crashes , what's the argument for not changing their locations, like wings or engines?
Given their utility after accidents, why not increase the redundancy even more by placing separate boxes in each engine for example.
I understand that military aircraft have jettisoned Recorders  that signal their location for recovery. Could this option be considered with Jettisoned Engines even before the crash in case of Extreme Load or excessive vibrations ?

There are some Deployable Black Boxes, but they are quite expensive and rarely needed.

The simplest argument to me is that no location on the aircraft is particularly special when it comes to locating black boxes in this sense. The recorders that aren't found are either in exceptionally remote locations or underwater - I don't see anything special about an engine that makes it more likely to be found than the wreckage of the fuselage.
No matter where you place them, there are going to be circumstances where they can't be found.

That is soon to be. Starting in 2019 Airbus is equipping the A350 with redundant, floating, jettisoned recorders. They will be in addition to the usual ones inside the aircraft.
None of the articles I've read indicate whether it's a standard feature or an option.

FDRs are already in the most survivable location, in the tail.  Look at any crash site and the tail cone is usually the only intact major component.
You don't want to jettison them because you need to record data right to the point of impact. The jettisonable devices that are used today are crash locator beacons, not data recorders.  They've been around since the 70s.
Ultimately what will make all this moot is that going forward all of the data that would be recorded by the FDR/CVR will be transmitted and recorded in real time via satellite... some day.
In theory, it could be possible to jettison an engine on a wing mounted engine aircraft, because they have fallen off on their own and the airplane was still flyable because there was little CG shift.  Hmmmm what about whoever is below this falling object the size of a single car garage, which may get discharged over populated areas with some regularity?

Regarding transmission of flight data to or via satellite, see Could the CVR and FDR record to the cloud?

Pretty much anything is possible but in commercial aviation things proceed at a snail's pace because of the cert process to bring any new system or concept to the market.  Large flat panel displays were common in corporate and general aviation many years before they finally started to appear in airliners.


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Will afterburner work at settings less than full dry thrust?
Dry thrust is normal jet engine power without using an afterburner. Max dry thrust is the engine's most powerful thrust level without afterburner.
But what if the engine is at half power, or even idle power? Can you safely engage afterburner at that point?
I'm interested in turbojets and turbofans. Both can have an afterburner. I'm wondering if it's possible to engage afterburner on both of them at a time when the engine is not already at full dry thrust.
Edit: one reason it might not work is that idle thrust might not be powerful enough to ignite the fuel in the afterburner.
The reason I ask is for emergencies. Jet engines need several seconds to spool up from idle to full thrust. If you could engage afterburner from the get-go, you could be up to max speed much quicker.

No need to include information from the answer(s) in your question. Most people will read the answer(s) and find the info there. ;)

Afterbuner simply injects fuel directly into the jet pipe (i.e. beyond the turbine) in order to greatly increase thrust. The way throttle levers are normally set up, afterburner is engaged once the lever is advanced past maximum dry thrust, but I can't imagine why, theoretically, you couldn't set one up to be engaged at less than maximum dry thrust.
Mind you, it would be awfully inefficient to do so, as thrust output is exponential, with most of it being delivered in the top 5% of the RPM band; engaging afterburner while you still have a lot of dry thrust available would just be a massive waste.
What's more, jet engines are much quicker to respond today, and, in addition, landing approaches are not performed at idle thrust; the main benefit of flap settings greater than 20 degrees is that they slow the aircraft down, allowing for steeper approaches. In jet aircraft, this also allows the engines to be kept spooled up above flight idle, specifically in order to reduce response times in the event of a go around.
In other words, throttle might be reduced to flight idle for the initial descent, but the final approach will use a higher thrust setting.
The benefits of adding afterburner to civilian transport aircraft are usually massively outweighed by their costs (see the Concorde and Tu-144).

Right, but I'm wondering if idle thrust would be enough to ignite the fuel in the afterburner. Made an edit to the OP.

@DrZ214 - We wouldn't know the answer to that unless we could get some temp readings from the exhaust pipe with thrust at idle; I do know that kerosene doesn't burn easily and that the ignition system used to start the combustion is very powerful. At any rate, I think the point is rather academic: advancing the throttle lever past full dry thrust would engage the afterburner and start fuel injection into the pipe; the fuel would start burning as soon as the exhaust temperature gets hot enough, while any unused fuel would simply be vented outside along with the exhaust gases.


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How much extra drag does landing gear incur?
How much extra drag does landing gear incur?
I'm interested in large commercial airplanes. For a concrete example, let's say a 747 flying at 1,000 m above sea level at 800 km/h. Edit: Looks like 800 kmh is too high for lowered gear at 1,000 m. Let's say 400 kmh instead.
In those conditions, what is the drag with the gear lowered, and what is the drag with the gear fully raised?
Drag is a force measured in newtons.

It is more than you may think being small in relative proportion. Barring any other configuration changes, lowering the gear feels like stomping on the brake pedal, which is (one of the reasons) why in an emergency you don't lower the gear until you have the field made.

Just a quibble, but the regulatory speed limit (in the US) at that altitude is 250 knots indicated.  That works out to about 490 km/h TAS.  I'm not even sure a 747 has enough thrust to go 800 km/h TAS at 1,000m...  Approach speeds are around 265 km/h CAS for a 747.

Interesting question, but this may just be a bit too broad of a question as it is largely dependent upon specific airframes.

@CarloFelicione I gave a concrete example: a 747 at 1000m above MSL at 800 kmh---corrected to 400 kmh.

But again, this is subjective and these figures vary from airframe to airframe.

It's enough drag that in flying a 747-100 gear down the 600 nautical miles from Yokota Air Force Base near Tokyo to Osan Air Force Base a bit south of Seoul, we burnt more than twice the projected fuel burn. Had we not been tankering fuel to avoid refueling at Osan, we would not have been able to do it when we couldn't get the gear up. It was all we could do initially to stagger up to FL190, and we never got higher than FL220.

@ymb1 No problem, happy to be of assistance.

There is one data point from real life: An Airbus A-310, scheduled to fly from Chania (Crete) to Hannover, Germany, a distance of 2197 kilometers, could not get the gear up after take-off on 12 July 2000. The crew decided to fly slower in order to conserve fuel and initially tried to divert to Stuttgart. When they realised that fuel flow was higher than anticipated, they reduced their trip planning first to Munich and then Vienna. On approach, while still 12 nm out from the airfield, the engines cut out and the aircraft landed just short of the runway, incurring damage beyond economic repair. None of the occupants were injured during the landing.
The distance from Chania to Vienna is 1545 km, and the aircraft used up all the fuel onboard, including reserves. This makes the distance flown about half of what would be possible with gear up and exhausting reserves. Since the added drag from the landing gear shifts the optimum range speed to a lower value, the aircraft had to fly not only slower, but also lower than normal, and a direct comparison of the drag with and without gear extended is impossible.


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What safety mechanisms prevent thrust reverser deployment in mid-flight?
I just came across the Wiki article on Lauda Air Flight 004, which was destroyed when a thrust reverser activated in mid-air.
In the article, it says:

The incident led Boeing to modify the thrust reverser system to prevent similar occurrences by adding sync-locks, which prevent the thrust reversers from deploying when the main landing gear truck tilt angle is not at the ground position.

But that can't possibly be enough. Landing gear is lowered and locked while the plane is still flying. That means these "sync-locks" would be released while the plane is still in the air.
Edit: Looks like I misunderstood what "not at the ground position" meant. Apparently the truck tilt angle is not flush except when the wheels have pressed onto the ground. Nevertheless, the general question of what safety mechs there are, still stands.
Are there any other safety mechanisms? Are there any that detect, somehow, that the wheels have actually touched down? Maybe a wheel RPM sensor?

I'm not sure if this a dupe, but there's a lot of overlap with these two questions: here, here

I'm just speculating from the text, but a 767's landing gear seems to be at an angle when it's in the air (see this image for an example of what I mean). So maybe the text is saying that the sync-lock looks at not just whether the gear is down, but its actual angle -- the assumption being that it will only be 90° (or whatever) when the airplane is actually on the ground, pushing down on it.

Many aircraft have a WOW (weight on wheels) switch.  It's commonly mounted on the oleo strut such that when the oleo is compressed, the switch is closed.

The truck tilt angle is not in the "ground position" when the gear is lowered. If you look at a landing aircraft, you can see that the trucks (the axles the wheels attach to) are at an angle. See this image for an example.

Safety is often a matter of tradeoffs. Lufthansa flight 2904 (an Airbus A320-200) had better safeguards against accidental deployment of the thrust reversers, which contributed to it overshooting the runway: Computer logic prevented the activation of both ground spoilers and thrust reversers until a minimum compression load of at least 6.3 tons was sensed on each main landing gear strut, thus preventing the crew from achieving any braking action by the two systems before this condition was met.

@yshavit Thanks, made an edit.

@chirlu Interesting. Someone mentioned a radio altimeter as one of the safety mechanisms. That alone seems like enough, and a much less complex solution, unless perhaps those altimeters are not reliable or have a high rate of inaccurate readings?

On a Boeing 777, the thrust levers need to be at their idle stops otherwise the thrust reverse levers physically cannot be moved aft. Once the thrust levers are at their idle stops and the  reverse levers are moved to the reverse thrust position there will be three signals provided to the thrust revereser actuation system (TRAS).
These three signals to the TRAS energize the thrust reverser sync lock valve
(SLV), the directional control valve (DCV), and the isolation valve (IV). At a reverse thrust lever angle of 11 degrees, the SLV is energized by closing a microswitch in the thrust lever assembly. The SLV then sends hydraulic pressure to the sync lock on each thrust reverser sleeve to accomplish release.
At 24 degrees reverse thrust lever angle, the DCV is energized by a microswitch in the control column assembly where the thrust levers and reverse thrust levers reside. The valve is shuttled by system pressure to the deploy position.
At thrust resolver angle of <31 degrees the IV is opened by a signal from the electronic engine control (EEC), and system pressure, by way of the DCV, is ported to the actuators. The IV command, from the EEC, also requires the engine to be running and the airplane to be on the ground.
Air/ground logic uses radio altimeter signals, with ground mode for the thrust reversers being < 5 feet. The locks within the locking actuators release and the thrust reverser sleeves move aft. After the thrust reverser sleeves move aft by a measure of 60%, interlock releases and the levers can then be moved to their maximum reverse thrust position.

The important bit in your wikipedia quote is

main landing gear truck tilt angle

as the gear trucks hang at an specific angle when not on ground. Take a look at this picture of a B767-300ER (same a/c type). You can clearly see the gear truck tilted forward.
It is not hard to imagine that the gear truck will be parallel to the fuselage after touch-down. Only then the reversers can be unlocked. When the gear is unloaded (aka the aircraft flies) the gear truck will take its forward tilted position, thereby inhibiting the reversers.
I don't know the exact engineering solution on the B767 but it is most likely the same as for the B747: a simple reed switch which closes when the gear truck is tilted at the correct angle. The switch is mounted on the gear strut and the magnetic target on the gear truck.
Truck tilts -> target comes close to the switch -> switch closes -> aircraft must be in the air -> no reversers for you.
EDIT: After you refined your question: Generally speaking there are different ways of sensing if the aircraft is on ground. All have their shortcomings. Here are some:

gear tilt (as explained above)
oleo strut compression (when the gear strut is compressed there must be weight on it, therefore the a/c must be on the ground)
radio altitude (when the radio altimeter senses zero or negative values the a/c must be on the ground)

The wheel RPM you suggested is not used - when you land on a wet runway there is a good chance you'll end up hydroplaning down the runway with load on the gear but no wheel rotation.
Airspeed is not used as well. Reverser deployment short final would be disastrous. And tying it to the stall speed (Vs) would be counterproductive as you touch down with a speed well away from Vs.
Hope this helps,
Chris


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If no low-speed compromises were made, what would an ideal Mach-3 wing look like?
Things like the Concorde and Tu-144 and many other supersonic craft need a wing that has good high-speed and good low-speed performance. After all, it needs to be able to take-off and land. Good low-speed performance is achieved with things like flaps, slats, and the wing shape itself.
But let's just say, hypothetically, you don't need good low-speed performance at all. So no such compromises in the wing shape. What would an ideal Mach-3 wing look like?
The goal is to have a wing with the highest lift-to-drag ratio at Mach 3.
I chose Mach-3 because that seems to be the limit on what jet aircraft have been put into production (MiG-31, SR-71) (which does not count experimental aircraft).
I'm interested in conventional designs, not things like the Blended-Wing-Body. So presumably this ideal aircraft would look similar to the Concorde or Tu-144.
Some things I've noted over the years:

The X-15 had a "wedge" shaped vertical stabilizer with a flat back. You can see it in photos. They said it was because the flat back produces more stability for less drag at high mach. Would a mach-3 wing also have a thick, flat trailing edge?
Ogival Delta seems very popular for large sophisticated supersonic aircraft. Never understood why that is exactly, since the pure delta triangle is easier to manufacture and bear loads easier.
The XB-70 Valkyrie had folding wings to give it anhedral, supposedly to capture the shockwave and thus be a wave-rider, which is more efficient. I've noticed the Concorde also has slightly drooping wings near the tips.

Note: I don't need a complete 3D model of the wing shape. I'm more interested in things like what planeform it has, what anhedral/dihedral if any, etc.

I'm not an aerodynamics engineer, but I suspect there's not a single "ideal" wing. Even if you did the airspeed, there are other parameters you need to trade off between. Do you want maneuverability, fuel efficiency, payload...

@yshavit Ah, don't need maneuverability. Was thinking simply to get the max lift-to-drag ratio. will edit.

I think this is a valid question; we know for subsonic flight the ideal wing is infinitely long and narrow, so how would it look for supersonic flight?

Looking beyond aircraft design into the design of large missiles may give a good indication of what such a craft might look like. Those are after all vehicles designed for such speeds, reached after a very short boost phase after launch which is typically performed during ballistic flight rather than controlled.

One Mach 3 design which did not care about low speed characteristics was the Lockheed Q-12 / D-21 reconnaissance drone, which used a Marquardt RJ-43 ram jet for propulsion and had a flight Mach number of up to 3.5. It was initially air launched from the back of an A-12 / M-21 and crashed when fuel ran out. The purpose was deep penetration of hostile airspace to perform photographic reconnaissance in pre-satellite days. When later the launch aircraft was switched to the B-52, the D-21 needed an enormous booster to bring it up to its cruising speed of Mach 3.35.
This should be closest to a uncompromising Mach 3+ design; however, it drew massively on the aerodynamic work with the A-12 / SR-71, so probably the solution space was restricted from the start.

D-21 three side view (picture source). The anhedral was needed to compensate for the rolling moment of the high tail in sideslip. An even more uncompromising design would had used a smaller vertical and an equal fin on the lower side and no anhedral. The lower side fin, however, would have made the air launch from the back of the A-12 impossible.
All surfaces had sharp trailing edges. A wedge-like cross section like the tail of the X-15 only starts to make sense at speeds in excess of Mach 5 when using drag for directional stability is more effective than adding more tail surface.

Wow that's quite a drone. Flight ceiling 29 km, speed Mach 3.35, range 5,550 km. My only concern is that stealth shape may have necessitated some compromise in the wing shape. I read the wiki article but all it had to say was The Q-12...used key technology from the A-12 project, including...radar cross-section reduction design features.

heh, so this ridiculous toy from my childhood was not as ridiculous!
http://www.3djoes.com/uploads/1/3/3/9/13396852/5617750_orig.jpg


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Which GPU (Graphics Processing Unit) is used to generate the graphics for avionics?
I guess it isn't the GTX 1080Ti.
But which GPU(s) has the Boeing 737-NG for example? How does it differ from a GTX 1080Ti (cost: around €800), or Quadro P6000 (cost: around €7100)? How many GPU's are required? And what is the cost of one single GPU-Module for a 737?

There's a reduced subset of OpenGL for safety-critical applications like aviation. The Mali-400 implements it, I believe, but I don't know what implementations are popular.

It isn't anything like your home computer graphics cards if that is what you are asking. It is manufacturer specific and may not even be a separate processor.

Real Aircraft displays do not use 'off-the-shelf' display adaptors. They will have some graphics processor (often developed by one of the major companies ATI/Nvidia) but this will often be an older/mature chipset. Each display also might have multiple graphic processors. The cost of an aircraft display is more closely related to the cost of developing/certifying the hardware/software than the physical cost of the components. You can't realistically compare an Aircraft display to your desktop PC.

Aircraft displays aren't just dumb monitors, each is a computing device in their own right that processes the data from the aircraft's systems. Each display will continue to work if another fails. Modern standards such as ARINC661 moves some of the processing/behaviour to other computing units, but the display unit itself is still responsible for drawing the graphics.

The component you are looking for is a "symbol generator" (sometimes SGU). That could be PowerPC chips (e.g. PPC 603e, RISC).

I feel like there is enough information in these comments to be combined into an answer.

Can someone explain the downvote?

I didn't downvote but there are a lot, probably an exhaustive amount, of questions on this exchange which have a certain presumption that in the belly of every aircraft lives a ruggedized version of some PC complete with graphics cards, some popular OS variant, etc... It's not that they're bad questions it's just that at the root is a truly misunderstood conception of how computing in aviation works. That's not necessarily anyone's fault, but it is a very common theme. Maybe analogously it's like me (an American) asking someone in England a cricket question but using baseball presumptions.

Real Aircraft displays do not use 'off-the-shelf' display adaptors. They will have some graphics processor (often developed by one of the major companies ATI/Nvidia) but this will often be an older/mature chipset. Each display also might have multiple graphic processors. The cost of an aircraft display is more closely related to the cost of developing/certifying the hardware/software than the physical cost of the components. You can't realistically compare an Aircraft display to your desktop PC.
Aircraft displays aren't just dumb monitors, each is a computing device in their own right that processes the data from the aircraft's systems. Each display will continue to work if another fails. Modern standards such as ARINC661 moves some of the processing/behaviour to other computing units, but the display unit itself is still responsible for drawing the graphics.

Welcome to aviation.SE!


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How to program an FMC if the database is missing the arrival airport?
Let's say you are in a 737 flying to Geita, Tanzania, as you can see this little airport/airstrip has an IATA code, but not an assigned ICAO code. What should you enter into the FMC if I want to fly to that airport?
And in general, how to navigate to an airstrip that has only an IATA code?

Just enter lat long.  The rest is the same.

You want to fly a 737 into a 2000 m x 22 m dirt strip? I'm pretty certain that Geita airport is VFR only, so if you were flying there as IFR, you would fly to a nearby navigation aid and then continue VFR.

It is about the FMC, I just picked a random airport

As I say, just enter the last navaid on your planned route, then lat long for the airport.

@J.Hougaard lol

@J.Hougaard -- 737s operate out of runways that size all the time points over at KMDW (although you are right that Geita's likely VFR only...)

@J.Hougaard, 2000 m runway is plenty for the smaller 737 variants (not for -900 though) and with track 5.75 m, 22 m width should be enough too.


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How to calculate the Pitching moment coefficient of wing?
I want to check the trim condition for aircraft. For this I need the pitching moment coefficient of wing. How to calculate?

Hi!  Welcome to Aviation StachExchange.  Are you able to be more specific.  What does the Wikpedia article not give you?

Take the pitching moment coefficient of the wing's airfoil at the trim angle of attack. Since the reference area normally is the wing's area and the reference chord is the wing's mean aerodynamic chord, you do not even need to adjust the number. I hope you have the airfoil polar at hand; if the wing uses several airfoils, take a volume-weighted average; volume being here the product of local area and chord. If the wing has a symmetric airfoil, the coefficient is zero, in most other cases it will be a small negative number.

Use XFLR5 to construct and simulate your a/c model. Adjust the inertial masses such that you achieve a trim angle in the acceptable region.